Control for electrical closing of circuit breaker



April 28, 1959 c. J. YARRICK CONTROL FOR ELECTRICAL CLOSING OF CIRCUITBREAKER Filed May 10, 1954 3 Sheets-Sheet 1- April 28, 1959 c. u.YARRICK CONTROL FOR ELECTRICAL CLOSING OF CIRCUIT BREAKER Filed May 10,1954 I5 Sheets-Sheet 3 NYN I INVHVTOR. 67/1445: Kill/ck United StatesPatent CONTROL FOR ELECTRICAL CLOSING OF CIRCUIT BREAKER Charles J.Yarrick, West Collingswood, N..l., assignor t0 I-T-E Circuit BreakerCompany, Philadelphia, Pa., a corporation of Pennsylvania ApplicationMay 10, 1954, Serial No. 428,638

3 Claims. (Cl. 31736) My invention relates to an automatic closing meansfor circuit breakers and is more particularly directed to a novelapparatus which incorporates a time delay in the drop out of the closingcontrol relay armature to prevent pumping operation.

It is frequently desirable to energize a closing relay and closing coilof a circuit breaker from the studs of the circuit breaker itself.

Heretofore, a pick up or closing relay construction has been usedwhereby the armature of the closing relay is latched to the controlmeans of the closing coil auxiliary contacts when the armature is in theneutral position.

Following the energization of the closing relay coil, the relayarmature, when moved to its engaged position, will move the auxiliarycontacts of the closing coil into engagement due to the latchengagement. However, movement of the closing plunger, following theenergization of the closing coil, will automatically unlatch theauxiliary contacts of the closing coil from the relay armature. Hence,even though the operator may continue to energize the closing relaycoil, the unlatching will prevent the continued energization of theclosing coil.

This arrangement has proved satisfactory in circuit breaker applicationswherein the closing apparatus and circuitry are energized and operatedfrom an auxiliary source of energy. However, a disadvantage isencountered when the closing circuit is energized from the line beingprotected by the circuit breaker. That is, in the event the circuitbreaker should be closed on a short circuit or low impedance fault, thevoltage will drop as soon as the arcing contacts come into engagement.The drop in voltage will thus cause the closing relay armature to dropout thereby permitting relatching between the relay armature and theauxiliary contacts on the closing coil.

Accordingly, if the operator continues to maintain the closing button inthe closed position, the closing coil will again be energized as therelay armature and auxiliary contacts are picked up. Hence, pumpingoperation results when the circuit is energized in the last mentionedmanner.

It is a primary object of my invention to provide closing means forcircuit breakers wherein the drop out of the closing relay armature istime delayed so that relatching is prevented in the event the circuitbreaker is closed on a low impedance fault.

I achieve time delay operation of the relay armature or plunger in oneof three ways.

In one embodiment of my invention, I provide a guide sleeve for therelay plunger which is made of a conducting material. Thus, when thearcing contacts of the circuit breaker is engaged and the line voltagedrops out, the collapse of the field of the relay coil will induce ashort circuit current in the short circuited secondary comprised of theconducting sleeve. Thus, this short circuited current in the sleeveguide will result in maintaining the relay plunger in the engagedposition for a predetermined length of time.

Tests have indicated that the time delay by this electromagnetic meanscan be obtained in the order of approximately one half second.

In a second embodiment of my invention, I provide a pneumatic time delayfor the relay plunger. In this arrangement, a non-conducting stationarysleeve is placed around the plunger of the relay.

A very small clearance is allowed between the plunger and the sleeve andthe end of the sleeve is sealed ofl. Thus, in the event that the biasingspring attempts to force the plunger to drop out of position, a vacuumwill be created thereby delaying the movement of the plunger to the openposition. By providing this air check for the relay plunger, I have beenable to obtain time delay of the magnitude of two and three secondsbefore the relay plunger drops out.

In a third embodiment of my invention, I combine embodiments 1 and 2wherein a conducting sleeve provides for electromagnetic time delay andthe close tolerance between the conducting sleeve and the relay plungerprovides for pneumatic time delay.

With the time delay of my invention, engagement of the arcing contactsresulting in a drop of the line voltage will not result in subsequentpumping. Since the main cooperating contacts of the circuit breaker willopen thereby restoring the voltage, the relay coil will again beenergized thereby holding the relay plunger in the engaged position andthus preventing it from relatching with the auxiliary contacts of theclosing coil. Hence, if the trip mechanism of the circuit breaker doesnot have a time delay, the time delay of the closing relay plunger needonly be longer than the period of time between the engagement of thecircuit breaker arcing contacts and their subsequent separation.

In the event the closing means is utilized in connection with a timedelay circuit breaker, then it is necessary for the time delay of therelay plunger to be longer than the time delay of the circuit breaker.That is, since the main contacts of the circuit breaker will be inengagement, that is, closed on a fault, the line voltage will drop outand hence, the relay coil will not be energized. However, by providingtime delay for the plunger which is longer than the time delay of thecircuit breaker, anti pumping operation is achieved. That is, aft r themain contacts of the circuit breaker separate, line voltage will againbe restored and hence, the closing relay coil will be energized to holdand maintain the relay plunger in the engaged position to preventrelatching.

Accordin ly, one object of my invention is to provide a time delayclosing relay plunger to prevent pumping operation of the circuitbreaker.

A further object of my invention is to provide electromagnetic timedelay for the plunger of a closing relay to prevent relatching in theevent the circuit breaker is closed on a fault.

Another object of my invention is to provide pneumatic time delay toprevent the reset of the closing relay to thereby insure anti pumpingoperation.

Still another object of my invention is to provide apneumatic-electromagnetic time delay for the closing relay which willmaintain disengagement of the latch between the relay plunger and theauxiliary contacts of the closing coil.

Still another object of my invention is to provide a closing means for acircuit breaker wherein a time delay is provided for the drop out of theclosing relay. The time delay period is provided for the closing relaywhich is greater than the time delay operation of the circuit breaker.

A still further object of my invention is to provide automatic closingmeans for a circuit interrupting equip ment which results in antipumping operation for both instantaneous and time delay circuitbreakers.

A still further object of my invention is to provide a circuit breakerclosing means energized from the line being protected by the circuitbreaker which can utilize either pneumatic or electromagnetic or acombination of these two for the time delay drop out of the relayplunger.

These and other objects of my invention will be apparent from thefollowing description when taken in connection with the drawings inwhich:

Figure l is an exploded perspective view of the operating mechanism of acircuit breaker showing the cooperating contacts in the disengagedposition. This figure also illustrates the latch controlled relay andthe closing coil controlled thereby.

Figure 2 is a side schematic view illustrating the automatic closingsystem used in connection with the circuit breaker of Figure 1. Thisfigure illustrates the position of the parts of the control relay and aclosing solenoid immediately following an attempt to close the circuitbreaker on a fault. This figure illustrates the trip free position ofthe circuit breaker.

Figure 2a is a cross-sectional view of the first embodiment of myinvention illustrating a close fit between a non-conducting sleeve andthe armature to achieve time delay by pneumatic means.

Figure 2b illustrates a second embodiment my invention wherein a loosefitting sleeve made of a conducting material is positioned concentricwith the armature to achieve time delay of electromagnetic means.

Figure 2c illustrates a third embodiment of my invention wherein aconducting close fit sleeve is provided for the armature to achieve timedelay by both pneumatic and electromagnetic means.

Figures 3 through 6 are schematic views of the circuit breaker ofFigures 1 and 2 illustrating the position of the various components forvarious positions of the circuit breaker.

Figure 3 illustrates the closed position.

Figure 4 illustrates the initial trip position.

Figure 5 illustrates the collapsed position.

Figure 6 illustrates the completely open position.

Referring now to Figure 1, under over current conditions, an energizedovercurrent coil pulls the armature 143 toward trip member 140. Thescrew 145 acts to rotate bar 140 upon the energizing of the overcurrentcoil by engaging extension plate 146 which is bolted to the shaft 140.The shaft 140 is caused to rotate in a counterclockwise manner lookingfrom the right of the circuit breaker, which is the view of Figure 1?The shaft 140 is also caused to rotate by means of a coil 150 which,upon being energized, attracts armature member 151. The link 152 isattached to an angle which in turn is movably attached to the member 151by means of a pin. A restoring spring 147 attached to the member 151resets the armature upon de-energization of the coil 150.

The link 152 is attached to the shaft 140 by means of another angle andcap 160.

Thus, the shaft 140 can be caused to rotate by two methods, one due tothe energization of an overcurrent trip coil and armature 143 and theother due to the energizing of the coil 150. The coil 150 may beremotely energized by manual operation of a remote push-button switch.The rotation of shaft 140 causes a link 162 to be moved by means of anangle 163 which is bolted to the shaft 140 by means of two bolts 164.The angle 163 has an indentation 165 near the farthest edge 166 from theshaft 140. The link 162 has two slots 168 and 1127. The slot 167 engagesthe indentation 165 of angle 1 3.

The translatory movement of link 162 causes the rotation of a milledshaft 170. The milled shaft 170 has another angle 171 rigidly attachedto it by means of two bolts 172. This angle has an indentation 173 nearthe end 174 which is farthest from the shaft 170. The indentation 173 ofangle 171 engages the slot 168 of link 162. Thus, the rotation of shaftcauses the rotation of milled shaft 170. When milled shaft rotates torelease a latch 177, as is hereinafter described, the circuit breakermovable contact 61 is allowed to be disengaged from the stationarycontact 60.

The angle 171 described above has an abutment 178. This abutment 178 isengaged by a roller 179 which is rotated manually by means of theclosing handle 184 attached to the shaft 180. Shaft 180 has a crank 181which is rigidly attached to the shaft 180 by means of a screw 182. Theroller 179 is attached to one end of the crank 171. When the shaft 180is rotated by the closing handle 184, the roller 179 engages abutment178 of angle 171 and rotated milled shaft 170. Thus, milled shaft 170can be made to rotate by a plurality of methods. It can be made torotate manually by means of closing handle 184; it can be made to rotateby means of an over current condition in the trip coil; and it can bemade to rotate by means of an excitation of coil 150, as describedabove.

The latch 177 is an integral part of trip arm 185. The latch 177 engagesthe milled shaft 170 so that a small revolution of shaft 170 releasesthe latch 177, as hereinafter described. The shaft 170 is milledslightly past center at 186. The trip arm 185 is pivoted at 187 on along pin 188. The pin 188 is also engaged on the trip arm extension 187at point 183. The pin 188 breaks a movable arm 190. The movable arm 190is pivoted on pin 188 at points 191 and 192 and extends beneath a roller193. The roller 193 is the pivot point of a toggle mechanism consistingof two links 194 and 195 and is carried by a pin 202 which pivots themeeting of links 194 and 195.

The links 194 and 195 each comprise two arms, 194A and 194B, and 195Aand 195B, respectively. Arms 194A and 194B are pivoted on floating pin196, described below, and arms 195A and 195B are pivoted on pin 204,also described below.

The arms 194A and 194B support a rod 197 at 198 and 199, respectively.The rod 197 carries one end of a restoring spring 203 which is tensed bymeans of a stationary shaft 212, hereinafter described. The restoringspring 203 exerts a tension on the link 194 which tends to open or breakthe toggle mechanism. Link 194 is pivoted on a floating pin 196 which issupported by link arm 185 and its extension 189 being parallel to thepin 188. The other link 195 of the toggle is pivoted on movable link 200which is connected by means of an adjustable insulator 201 to themovable contact assembly 61, described below.

When the toggle mechanism consisting of links 194 and 195 isstraightened out by means hereinafter described, pressure is put onmovable link 200 by means of link 195 and bearing pin 204. The movablelink 200 is pinned to insulator 201 by a pin 205 and moves so as toadvance the insulator 201 and the movable contacts 61 towards thestationary contact 60.

In the exploded view shown in Figure 1, the contacts are open and thetoggle mechanism consisting of links 194 and 195 is collapsed. Thecircuit breaker may be closed by a variety of methods. The circuit canbe closed manually by means of shaft 180 rotated by closing handle 184,described above. If shaft 180 is rotated in the direction indicated bythe arrow 184A, the roller 179 will engage the bottom of arm 190 andforce the arm 190 against roller 193, thus straightening out the togglemechanism and closing the circuit breaker contacts.

The movable links 200 are under an opening tension by means of openingspring 210 so that if no additional locking action other than describedabove for supporting the toggle existed, the circuit breaker wouldreopen immediately upon releasing the shaft 180. The locking device .issupplied by means of a crank 211 which is located on a shaft 212,mentioned above, whose longitudinal axis is parallel to the axis of themilled shaft 170 open, adjacent the roller 193. When the roller 19.3

Is-forced upward, as due to the pressure of arm 190, the

roller pushes against arm 213 ,of crank 211 rotating the crank 211slightly on shaft .212. When the roller 193 has cleared the top of arm213, the arm 213 snaps underiieath the roller 193 due to the compressionof a spring 220. The spring 220 which is wound .on the shaft 212 has oneend on an indentation 221 of crank 211 and the other end borne against ashaft 222 which pierces the t-riparm 185. The shafts 212 and 222 havebeen moved out of position in the exploded view for the sake of clarity.Actually, the shaft 222 pierces the trip arm 185 at point 207. Thelongitudinal axis of shaft 222 is essentially parallel to thelongitudinal axis of shaft 212 andmilled shaft 170.

When the roller 193 is moved, straightening the toggle, it causes crank211 to rotate compressing spring 220. The roller clears the top of arm213 letting the crank rotate in the opposite direction until the arm 213is directly be eath and supporting the roller 193. The other arm 214 ofcrank 211 bears against the shaft 222 preventing further rotation of thecrank 211 so that the arm 213 is stopped directly beneath the roller193. The spring 220 is under compression normally so that the arm 214 isconstantly bearing against the shaft 222. When the toggle isstraightened, the rotation of the crank 211 moves the arm 214 away fromthe shaft 222 until the roller 193 clears the top of arm 213. Then thereverse rotation of the crank 211 occurs until the arm 214 again bearsagainst shaft 212.

Thus, when the toggle is straightened, and the circuit breaker closed,the crank 211 locks the toggle and thus locks the circuit breaker in aclosed position.

The closing handle 184, by means of the shaft 180, after closing thecircuit breaker by means of the rotation of roller 179 against the arm190, as described above, is returned to its normal position by means ofa crank 230. The crank 230 is pivoted on a stationary pin 231.

The crank 181, described above, has an indentation 232 which meets aroller 233 of crank 230. The crank 230 supports a pin 234 which has arestraining spring 235 engaged at one end 236. The restraining spring235 is attached to an angle 237 and is tensed on the pin 236 causing thecrank 230 to rotate. The rotation of crank 230 causes the roller 233 tomeet the indentation 232 returning the crank 181 to its normal position.

The various positions of the operating mechanism are shown in Figures 3through 6.

Figure 3 shows the closed position thereof with link 1 95 pushed forwardto raise the crank 200 and close the contact arm or insulator 201 andwith the roller 193 on the arm or abutment 213.

The latch arm 185 is shown in appropriate latching engagement with themilled shaft 170.

When the shaft 180 described above is turned to release the mechanism,the condition as shown in Figure 5 W l Qn the occurrence of trippingconditions, the milled shaft 170 is rotated to permit the latch arm 185to move into the milled section of position 186 of the milled shaft 170,as seen in Figure 4. Then as seen in Figure 5, the roller 193 drops offthe abutment 213 to open the circuit breaker.

Thereafter, as seen in Figure 3, the latch arm 185 is restored to itsinitial position and the milled shaft 170 is restored to latchingposition so that the circuit breaker may again be moved from the openposition of Figure 6 to the closed position of Figure 3.

The circuit breaker may also be closed by means of the closing mechanismshown in Figures 1 and 2. The

6 closingmechanismis comprised of the control relay and .theclosingsolenoid.

The control relay is comprised of the coil 300 which is energized fromthe studs of the circuit breaker through the closing button 500. Thatis, the control relay is energized from the same source which is beingprotected by the circuit breaker.

The relay is of the latched type described in copending applicationsSerial No. 254,349, filed November 1, .1951, now Patent No. 2,792,534,Serial No. 383,714, filed Octoher 2, 1953, and Serial No. 423,782, filedApril 16, 1954, now Patent No. 2,832,917.

The control relay illustrated in Figures 1 and 2 differs from the relayset forth in the above noted copending applications in that the armature.of the relay is of -a plunger type which moves in and out of thecontrol coil 300. Also, the relay incorporates my novel time delay meanswhich will maintain the plunger type armature in its energized positionfor several seconds after the control relay is de-energized. Except forthese two distinctions, the control relay with its function andoperation are the same as set forth in the above identifiedapplications.

A brief review of this structure follows.

The cooperating contacts 308-502 which control the energizing circuitfor the closing coil 241 are carried by the bracket 306. The bracket 306and the extension 301 of the armature 312 are latched together by thescrew 324 and shaft 326 when these two components are in the normalposition illustrated in Figure l.

The spring 513 biases the bracket 306 around the pivot 302 to theneutral position and the biasing spring 523 biases the armature 312 andits extension 301 about the same pivot 302 to its neutral position.

When the closing button 500 is moved from its normally open position tothe closed position in order to initiate a closing operation, the coil300 of the control relay is energized from the line 517-578 beingprotected by the circuit breaker. Thus, the energizing circuit for thecontrol coil is through the lines 519-520, the regulator 525 to thecontrol coil 300.

Since the bracket 306 is latched at 324-326 to the armature 312-301,these two units will be moved to their energized position. The forwardmovement of the bracket 301 will result in the closing of the contacts308-502 thereby completing the energizing circuit for the closing coil241 of the closing solenoid.

Energization of the closing coil 241 will result in the upward movementof the closing plunger 240 and its extension 320-322, as best seen inFigure 2, to thereby close the breaker through the operating mechanismheretofore described.

The extension 322 of the closing plunger will engage the head 323 of thescrew 324 thereby unlatching the bracket 306 from the armature 312-301.Hence, the bracket 306 will now be influenced by its biasing spring 513and be moved to its neutral position, when the movement of the bracket306 to its neutral position will interrupt the energizing circuit forthe closing coil 241 by the opening of the contacts 308-502. Hence, ifthe control relay and closing solenoid are energized from an auxiliarysource, this unlatching operation will prevent pumping of the circuitbreaker even though the operator may continue to depress the closingbutton 500.

However, as will hereinafter be more fully described, additionaldifficulties are encountered when the closing means is energized fromthe source being protected by the circuit breaker.

After the circuit breaker has either latched closed, it will remainclosed if it is closed on circuit carrying normal load current or willhave strip free operation if it is closed on a line having a fault. Theposition of the components in Figure 2 illustrate the last mentionedtrip free operation.

Since the energizing circuit for the closing coil 241 is interrupted bythe movement of the bracket 306 to its the line being protected by thecircuit breaker.

' neutral position, the closing plunger 240 will fall back to thearmature 312301 by means of the screw 324 and the pin 326.

Accordingly, all of the components will now be in their neutral positionso that a subsequent intentional closing operation can be performed whenthe closing button 500 is reclosed.

As heretofore noted, my invention is particularly directed to a closingmechanism which is energized from In this type of arrangement, thecircuit breaker may be closed on a low impedance fault. Hence, eventhough the closing button 500 is maintained by the operator in itsclosed position, there will be a drop in voltage at the instant ofengagement of the circuit breaker cooperating contacts 6061 to therebyremove the energizing voltage for the control coil 300. If thissituation exists, the biasing spring 523 will move the armature 312-301to its neutral operations may be performed if the operator holds theclosing button 500 in closed position for one or two seconds. That is,there will be pumping of the circuit breaker even though the operatoronly intended a single closing operation.

My invention is directed to a novel means whereby a time delay isintroduced to control the drop out of the control relay armature toprevent pumping operation even though the operator may maintain theclosing button in the closed position for one or two seconds immediatelyfollowing trip free operation.

That is, in a circuit wherein the closing means are energized from thestuds of the circuit breaker, my invention intentionally introduces atime delay of two or three seconds for the drop out of the control relayarmature to thereby prevent relatching with the contact carrying bracketuntil the operator has released the closing button.

The time delay is introduced by one of three methods-(a) pneumaticmeans, (12) electromagnetic means, combined pneumatic andelectromagnetic means.

In the pneumatic time delay, a non-conducting sleeve 524, preferablymade of brass, is positioned between the coil 300 and the armature 312.The cylindrical sleeve 524 and the cylindrical armature 312 are providedwith a very close fit with a clearance of approximately 0.0025" betweenthe armature and the sleeve.

A check valve 525 is provided at the end of the armature.

After the voltage on the control coil 300 has been removed, the biasingspring 523 will attempt to move the armature 312 to its neutralposition. However, due to the very close fit between the armature 312and its encompassing non-conducting sleeve 524, a vacuum will be createdin the space 526 to thereby prevent the immediate removal of thearmature from the sleeve. However, after a two or three second delay,there will be a sufiicient drop of pressure in the area 526 to open theair check valve 525.

, As soon as the air check valve 525 is opened, the armature 312 willimmediately be moved to its neutral position by its biasing spring tothereby allow relatching of the brackets 306 with the armature 312-301in the manner heretofore described.

The cross-sectional view of Figure 2a illustrates the relative positionsof the coil 300, the non-conducting sleeve 524 and the armature 312. Thespace 527 between the armature 312 and the non-conducting sleeve 524a is0.0025".

In the second embodiment of my invention, I provide an arrangementwherein the sleeve around the armature 312 is made of a conductingmaterial such as copper. In this arrangement, the cross-sectional viewof which is shown in Figure 2b, the movement of the armature 312 isdelayed by electromagnetic action rather than pneumatic action so that alarge clearance can be provided between the armature 312 and theconducting sleeve 52417.

The operation of the second embodiment is as follows.

When the voltage for the coil 300 is removed, the magnetic field willcollapse thereby inducing a voltage in the conducting sleeve 5241).Since the sleeve 524b represents a shortcircuited secondary winding forthe control coil 300, a shortcircuit current will flow thereinimmediately following the de-energization of the control coil 300. Theflow of shortcircuit current in the conducting sleeve 524b will tend tohold and maintain the armature 312 in its energized position against theforce of the biasing spring 523.

I have found that I can introduce a time delay of onehalf to one secondby this electromagnetic means.

In the third embodiment of my invention, I provide .a combination ofpneumatic and electromagnetic time delay for the armature control relay.Thus, the structural arrangement is similar to that heretofore describedin connection with the pneumatic time delay. However the sleeve 524 isnow made of a conducting material.

The cross-sectional area of this embodiment is shown in Figure 20wherein the sleeve 5240 is made of a conducting material such as copper.Hence, time delay for the drop out of the control relay armature 313 isachieved as a result of the close fit vacuum and air check valve andalso as a result of the shortcircuit current which now flows through theconducting sleeve. Hence, the sleeve 5240 introduces time delay by bothpneumatic and electromagnetic means.

In the foregoing, I have described my invention only in connection withpreferred embodiments thereof. Many variations and modifications of theprinciples of my invention within the scope of the description hereinare obvious. Accordingly, I prefer to be bound not by the specificdisclosure herein but only by the appending claims.

I claim:

1. In a circuit breaker having a pair of cooperating contacts movablebetween an engaged and disengaged position and connected in series withan electrical system; said circuit breaker having a solenoid operatingmechanism comprising a solenoid plunger and an operating windingtherefor, said solenoid plunger being operatively connectable to atleast one of said pair of cooperable contacts for moving said cooperablecontacts to their said engaged position responsive to energization ofsaid operating winding; a control relay for controlling the energizationof said operating winding; said control relay comprising a first and asecond cooperating relay contact movable between an engaged anddisengaged position, a contact arm for carrying said first cooperatingrelay contact, a relay armature, and a relay winding; said relayarmature being positioned with respect to said relay winding to be movedfrom a first position to a second position responsive to energization ofsaid relay winding; said contact arm being biasedto move said firstrelay contact to a disengaged position with respect to said second relaycontact, said relay armature being biased to its said first position; alatch means; said latch means operatively connecting said armature tosaidcontact arm, said contact arm being movable with said reiay armaturewhen said latch means is in a latched condition; said latch means beinglatchable only when said relay armature is in its said first positionand said contact arm is in said position to maintain said first relaycontact in said disengaged position; said solenoid plunger beingconstructed to defeat said latch means when moved by said operatingwinding to engage said circuit breaker cooperating contacts; a closingcontact; said closing contact being connected in series with a voltagederived from said electrical system containing said circuit breaker andsaid relay winding; said operating winding being connected in serieswith a voltage derived from said electrical system containing saidcircuit breakers and said first and second relay contacts; and atime-delay means; said time-delay means being operatively connected tosaid relay armature and elongating the time required for said relayarmature to move from its said second position to its said firstposition after deenergization of said relay winding to delay the timesaid relay armature and said contact arm relatch after closing of saidcircuit breaker by said closing contact and deenergization of said relaywinding.

2. The device of claim 1 wherein said time-delay means comprises a shortcircuited Winding surrounding said armature.

3. The device of claim 1 wherein said armature is formed of a plunger;said time-delay means comprising a sleeve structure surrounding saidplunger to pneumatically time delay movement of said plunger.

References Cited in the file of this patent UNITED STATES PATENTS1,885,157 Traver Nov. 1, 1932 2,064,657 Goff Dec. 15, 1936 2,157,810Bany May 9, 1939 2,304,865 Thumim Dec. 15, 1942 2,346,147 Boisseau Apr.11, 1944 2,534,115 Favre Dec. 12, 1950

